Ability to write both II and MM type tiff images. Yes that's right you can write little and big endian images using the library.

I think this feature may prove useful when an application seeks to append images to an existing TIFF file on a machine that has different byte ordering than the original. This is not normally
possible since the byte ordering is file wide.

Providing this feature in libtiff would in my view increase it's machine independence. It could make the append mode of TIFFOpen() more robust.